Up to now, a disc cartridge comprised of a disc-shaped recording medium, such as an optical disc, a magneto-optical disc or a magnetic disc, arranged for rotation within a main cartridge member, has been extensively used. This sort of the disc cartridge accommodates a disc-shaped recording medium, on which information signals, such as audio or video signal or program data have been already recorded or are to be recorded. The disc-shaped recording medium, on which the information signals can be recorded, may be enumerated by a write-once disc, which allows to record the information signals only once, and a rewritable optical disc, such as a magneto-optical disc, which allows for re-recording information signals.
As a disc cartridge, accommodating therein a disc-shaped recording medium on which information signals have been already recorded or are to be recorded, such a one shown in FIG. 1 is in use. A disc cartridge 500, shown in FIG. 1, accommodates an optical disc 502, which enables information signals to be recorded, and includes a main cartridge body unit 501, made up by an upper shell 501a and a lower shell 501b, and an optical disc 502 rotatably housed therein. The upper shell 501a and the lower shell 501b, making up the main cartridge body unit 501, are each formed with a recording and/or reproducing aperture 503 for exposing a portion of the optical disc 502 to outside. On the main cartridge body unit 501, there is movably mounted a shutter member 504 for opening/closing the aperture 503. Centrally of the optical disc 502 is mounted a chuck plate 505 for chucking on a turntable of a disc driving device, which is adapted for rotationally driving the optical disc 502.
When the disc cartridge 500 is mounted in a cartridge mounting position in the disc driving device, the shutter member 504 is slid to open the recording and/or reproducing aperture 503, while the optical disc 502 is loaded on the turntable. At this time, the chuck plate is sucked by a magnet provided on the turntable, so that the optical disc is now able to be rotated in unison with the turntable. If then a spindle motor is run in rotation, the optical disc 502 is rotated at a constant linear velocity. At this time, the shutter member 504 is moved, so that the optical head faces the optical disc 502 via the opened recording and/or reproducing aperture 503. As the optical head is moved radially of the optical disc 502, and a signal recording area of the optical disc 502 is scanned by a light beam radiated from the optical head, the information signals recorded on the optical disc 502 are read out by the light beam radiated from the optical head, or the information signals are recorded on the optical disc 502.
Meanwhile, in an optical disc, accommodated in a disc cartridge, the recording density tends to be increased, in keeping pace with the increasing recording capacity, such that the recording pattern tends to be narrowed in pitch, while tending to be higher in line density. If, with the optical disc in which the recording density is increased in keeping pace with the increasing recording capacity, dust and dirt of minute size become affixed to the signal recording surface, the light beam from the optical head is thereby interrupted to disable correct recording and/or reproduction of information signals.
With the above-described conventional disc cartridge 500, since the shutter member 504 of a substantially U-shaped cross-section is fitted on the outer side of the main cartridge body unit 501 so as to be movable relative to the main cartridge body unit 501, there is likely to be produced a gap intermediate the main cartridge body unit 501 and the shutter member 504, such that intrusion of dust and dirt cannot be prohibited satisfactorily. As a consequence, dust and dirt are intruded into the inside of the main cartridge body unit 501 so as to be deposited on the optical disc accommodated therein.
With this disc cartridge 500, in which the shutter member 504 is mounted outside the main cartridge body unit 501, there is a fear that the user inadvertently moves the shutter member 504 to open the recording and/or reproducing aperture 503. Since the shutter member 504 is linearly moved along a lateral side of the main cartridge body unit 501, the size ratio of the shutter member 504 relative to the main cartridge body unit 501 is increased, so that it is difficult to reduce the size of the shutter member 504 and of the main cartridge body unit 501.